TwinTurbo.NET: Nissan 300ZX forum - Erratic idle speed help request
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Subject Erratic idle speed help request
Posted by jeff1954 on July 09, 2018 at 9:24 PM
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Message Mine is a 1991 300ZX non-turbo (California car), owned since February 1995, 137K mileage, with it's smog inspection due by August 14th. For about a year, been dealing with erratic idle speed, sometimes hovering around 1800 rpm, sometimes 1200 rpm, sometimes it idles correctly. Seems like after a freeway run, it occurs more (heat ?). Still though, it's very random. AAC and IACV were replaced, with new silicone hoses, coolant temp sensor was R2'd recently as well. Today, put the ECU in diagnostic mode, received code 55, " No malfunctions". Slaved in a different stock ECU (from an automatic), slight improvement in returning to normal idle, but still sometimes hanging at around 1800 rpm. Normally, replacing the IACV would fix this problem, but not this time. High idle speed will be a smog inspection fail. Aside from the erratic idle situation, the car runs just fine. Starting to wonder if this could be caused by the TPS ? But again, no stored codes, and no CEL. Any forum members have a similar experience ? And what was a good fix ?

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